The INSERT into template_trees incorrectly referenced `tags` as a column
on the `trees` table. Tags are a relationship via the `tree_tag_assignments`
join table — there is no direct column. Migration was failing with:
UndefinedColumn: column "tags" does not exist ... FROM trees
Fixed by replacing COALESCE(tags, '[]') with a correlated subquery that
aggregates tag names from tree_tag_assignments → tree_tags.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
d2ebc4f182